For advancement of ultra-high-density electronic devices, finer resolution patterning techniques and tools may be useful. Next generation lithography (NGL) candidates, for example, extreme ultra violet lithography (EUVL), electron beam projection lithography (EPL), and proximity electron beam lithography (PEL), are competing to become major tools for sub-65 nm patterning. Recent trends seem to indicate that EUVL and EPL are the strongest NGL candidates; however, the costs of prototypical tools may be high.
A proximity electron beam lithography (PEL) technique, which may use a 1:1 (or 1×) projection exposure of the resist material, has attracted much attention due to its relatively mature technology and substantially reduced cost projected for such a system. Ion beam or x-ray based lithography approaches are also based on a 1:1 stencil mask printing, like PEL, but electron beam based PEL technology may be more appealing due to its mature technology and industry-friendly system configuration.
The concept of PEL has been recently revisited and successfully implemented in a more modern format as a low energy electron beam proximity projection lithography (LEEPL) system. Progress has been made in various fabrication technologies and supporting infrastructures, for example, (1) thin-film resist materials compatible with low-energy electrons at several keV regime, (2) fine-featured stencil mask fabrication; (3) high-performance electron-beam writers for delineating circuit patterns on a mask; and/or (4) backbone technologies for high precision alignment and stage systems that are compatible with a high-vacuum environment inherent to the use of electron beams.
In contrast to 1:4 demagnifying EPL methods, which may require complex and/or expensive projection lenses, PEL employs real-size printing with the use of a stencil mask placed as close as approximately 30 μm above a wafer. In current PEL technology, a conventional hot electron cathode, which has a point source form, may be used and may limit the system downsizing and cost reduction. Relatively recent cold cathodes, for example, field emitter arrays (FEAs), photocathodes, and/or tunneling cathodes (metal-insulator-metal or metal-insulator-semiconductor structures), have desirable characteristics for vacuum microelectronic devices, for example, a large projection area (>1 mm2) emission capability, a small energy spread (<0.5 eV), and/or highly directional nature of the electrons (directed normal to the resist layer surface). Compared with conventional electron sources, the properties associated with cold cathodes may simplify electron optics and/or reduce the system cost.